Abstract:ABSTRACT. The aim of this study is to develop an analogical modeling methodology for IP and resistivity. Simple geometrical cylindrical and tabular shapes were built using standard cement, quartzitic sand and graphite. The experiment was carried out with various amounts of graphite in order to measure the IP response for different model geometries. The results are discussed in terms of IP response as a function of geometry, graphite content, depth and strike of the models.Keywords: Analog modeling; IP, resisti… Show more
“…and Wenner (Gallas & Verma, 2006;Gallas, 1990) in analog modeling, in laboratory-developed analog modeling under fully controlled conditions, show that the target detection depth can be even greater than the Hallof's (1957) depth. Measured parameters were Vp (primary voltage), RPS (Relative Phase Shift)…”
Section: Drilling 34mmentioning
confidence: 98%
“…As measurements were always taken every 2 cm (dipole-dipole with AB=MN=2cm), and constant current, Vp measurement has the same meaning as resistivity. In addition to this modeling, dozens of others were partially presented in Gallas & Verma (2006) and their full version is in Gallas (1990). Models were placed at depths of 0.5, 1.0 and 2.0 cm.…”
The article presents considerations on the depths achieved by Vertical Electrical Soundings (VES) as a function of electrode distances, and also on their quantitative interpretation. Besides the distances among electrodes, the effective achieved depths will depend on the resistivity distributions. At the request of environmental agencies, resistivity geophysical surveys were carried out in an area designed to the implementation of a residential complex which, would have to present a site hydrogeological study, including a potentiometric map among other requirements to be met. For the referred map elaboration, 18 VES were carried out in order to determine the depth of the water level at these points. In addition to this information, the works provided another additional data: the determination of the bedrock depth. Based on VES results, the potentiometric map and the bedrock depth map were elaborated in the study area. The cost reduction with the use of this indirect technique is significantly lower when compared to the costs of mechanical soundings, besides the reduction of the execution time.
“…and Wenner (Gallas & Verma, 2006;Gallas, 1990) in analog modeling, in laboratory-developed analog modeling under fully controlled conditions, show that the target detection depth can be even greater than the Hallof's (1957) depth. Measured parameters were Vp (primary voltage), RPS (Relative Phase Shift)…”
Section: Drilling 34mmentioning
confidence: 98%
“…As measurements were always taken every 2 cm (dipole-dipole with AB=MN=2cm), and constant current, Vp measurement has the same meaning as resistivity. In addition to this modeling, dozens of others were partially presented in Gallas & Verma (2006) and their full version is in Gallas (1990). Models were placed at depths of 0.5, 1.0 and 2.0 cm.…”
The article presents considerations on the depths achieved by Vertical Electrical Soundings (VES) as a function of electrode distances, and also on their quantitative interpretation. Besides the distances among electrodes, the effective achieved depths will depend on the resistivity distributions. At the request of environmental agencies, resistivity geophysical surveys were carried out in an area designed to the implementation of a residential complex which, would have to present a site hydrogeological study, including a potentiometric map among other requirements to be met. For the referred map elaboration, 18 VES were carried out in order to determine the depth of the water level at these points. In addition to this information, the works provided another additional data: the determination of the bedrock depth. Based on VES results, the potentiometric map and the bedrock depth map were elaborated in the study area. The cost reduction with the use of this indirect technique is significantly lower when compared to the costs of mechanical soundings, besides the reduction of the execution time.
“…Gallas & Verma (2006) abordam as profundidades de investigação, entre outras variáveis (mergulho, teores de material polarizável (Polarização Induzida -IP), espessuras etc), empregando modelos físicos cilín-dricos e tabulares para modelagem analógica de resistividade (e IP) em laboratório. Gallas (2003) obteve resultados que demonstram a eficácia da eletrorresistividade e sugere aberturas mínimas de dipolo com base na expectativa da profundidade a que se encontram os alvos da prospecção -zonas falhadas/fraturadas sob cobertura de alteração em área de ocorrência de rochas cristalinas em São José do Rio Pardo/SP.…”
Resumo: Levantamentos geofísicos de eletrorresistividade com arranjo dipolo-dipolo em áreas de ocorrência de rochas granito-gnáissicas foram realizados visando a detecção de estruturas do tipo falhas/fraturas ou outras de interesse hidrogeológico. Os resultados obtidos permitiram identificar estruturas que, em perfurações subsequentes, resultaram em 2 poços com excelente produção de água. Um terceiro poço foi perfurado, mas em local onde a assinatura geofísica poderia refletir um depósito de tálus, potencial bom aquífero ou rochas xistosas, potencial mau aquífero, sendo confirmada esta segunda possibilidade.
Palavras-chave:Resistividade. Água subterrânea. Aquíferos fraturados.Abstract: Geophysical resistivity surveys in granite-gneiss rocks, with dipole-dipole array, were carried out to detect fault/fracture structures or other of hydrogeological interest. The geophysical data allowed the identification of structures that in subsequent drilling resulted in two wells with excellent production volumes of water. A third well was drilled at a local where the geophysical data revealed an ambiguous geophysical signature which could reflect a talus, potentially a good aquifer, or a schist rock, potentially a bad aquifer, which was indeed confirmed.
“…These inversion processes were used in the treatment of the survey dipole-dipole data by using the software RES2DINV by ABEM Instruments (ABEM, 1998), based on the algorithm developed by Loke & Barker (1996a, 1996b, whose investigation depths (software default) are according to Edwards (1977) proposal, and also they are about half estimated (Hallof, 1957) but they can be modified by software user. Gallas & Verma (2006) and Gallas (1990) address the investigation depth issue, among other variables (dip, polarizable…”
Section: Modeled Pseudosections and Sectionsmentioning
ABSTRACT. Geophysical surveys were accomplished in Bahia, Brazil, and they aimed at detecting resistivity and/or IP geophysical anomalies that may be correlated to large quartz mass occurrences that, in some cases, may have economic interest (hyaline high-quality quartz or quartz with rutile inclusions). These quartz masses occur in granitic rocks. The indirect geophysical detection of quartz masses was possible, however it could not differentiate the aforementioned types of quartz. After digging wells and trenches, the presence of milky quartz masses, without economic interest, was confirmed.Keywords: resistivity, IP, quartz prospecting. RESUMO. Os levantamentos geofísicos foram efetuados no interior da Bahia, Brasil, e tiveram como objetivo a detecção de anomalias geofísicas de resistividade e/ou IP que pudessem ser correlacionáveis às ocorrências de grandes massas quartzosas que, em alguns casos, podem conter quartzo de interesse econômico – quartzo hialino de boa qualidade ou com inclusões de rutilo. Estas massas quartzosas estão contidas em rochas de composição granítica. A detecção de massas quartzosas por meios geofísicos indiretos foi possível, contudo não permitiu diferenciar os tipos de quartzo supracitados. Conforme confirmações posteriores com escavação de poços e trincheiras, os resultados detectaram a presença das massas quartzosas, porém de quartzo leitoso, sem interesse econômico.Palavras-chave: resistividade, IP, prospecção de quartzo.
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